In a system architecture evolution (SAE)/long term evolution (LTE) network, the S1 interface is an interface between an evolved universal terrestrial radio access network (eUTRAN) and a core network node (CN node). The CN node includes a mobility management entity (MME) and a user plane entity (UPE). The S1 interface is categorized into control plane interface (S1-CP) and user plane interface (S1-UP). The S1-CP is an interface between the eUTRAN and the MME (a control plane entity); the S1-UP is an interface between the eUTRAN and the UPE.
In the SAE/LTE network, between an evolved NodeB in the eUTRAN (eNodeB) and the MME, the logical connection between two S1-CP application part entities is called an S1 signaling connection, where the S1-CP application part is the S1 control plane interface application part protocol. In a current SAE/LTE network, the Stream Control Transmission Protocol (SCTP) is adopted as the transmission protocol for S1 interface control plane signaling. The S1-CP protocol stack is shown in FIG. 1.
As shown in FIG. 1, the evolved Radio Access Network Application Part protocol (eRANAP) entity is the S1-CP application part entity. To route application signaling over an SCTP transmission link correctly to the S1-CP application part entity, it is necessary that a one-to-one mapping should exist between transmission links and S1 signaling connections. Currently, mapping methods include the following two methods.
Method 1: Use the payload protocol identifier (PPI) field in the SCTP header to transmit identifier information of an S1 signaling connection in the following steps:                1) When a non access stratum (NAS) signaling connection is established, the eNodeB or MME allocates an S1 signaling connection ID to each user equipment (UE). The S1 signaling connection ID may be allocated by the entity that initiates the NAS signaling connection. The S1 signaling connection ID is carried in the first NAS message over the S1 signaling connection and transmitted to the peer node. For example, the S1 signaling connection ID is included in an Initial UE Message of the S1 application layer signaling and transmitted by the eNodeB to the MME. The eNodeB and the MME must save the S1 signaling connection ID within the lifetime of the S1 signaling connection.        2) The eNodeB and the MME respectively allocate communication instances for the new S1 signaling connection, which is uniquely identified by the SCTP association between the two ends, the SCTP stream, and the S1 signaling connection ID. 3) When the eRANAP communication entity of the eNodeB wants to send a message to the eRANAP communication entity of the MME, the eNodeB fills the S1 signaling connection ID in the PPI field of each SCTP data block and sends the message to the MME via the SCTP protocol.        4) The MME routes the message correctly to the communication instance of the S1 signaling connection according to the PPI field in each SCTP data block.        
Method 2: As shown in FIG. 2, respective communication context identifiers, that is, MME communication context identifier (e.g., AP MME/UPEcomm.id1, AP MME/UPEcomm.id2, AP MME/UPEcomm.idn, etc.) and eNB communication context identifier (e.g., AP eNBcomm.id1, AP eNBcomm.id2, AP eNBcomm.idn, etc.), are allocated to the eNodeB and the MME. The eNodeB or MME carries the corresponding communication context identifier in each application layer signaling message, and the peer application layer signaling entity routes the signaling message to the correct communication entity according to the communication context identifier.
During handover process, after a handover occurs, it is necessary to establish an S1 signaling connection between the target eNodeB and the evolved packet core (EPC) to connect the target eNodeB and the EPC.